As the ligaments of the foot and ankle age, fall prone to disease, or suffer trauma, their mechanical properties change. These changes profoundly influence how the involved joints function, and the mobility, comfort, and patient's level of activity and overall quality of life. This study seeks to develop a means of classifying the mechanical behavior of ankle ligaments based on age demographics (younger: 25-40 years old and older: 60-75 years old populations), ligament size (e.g., from magnetic resonance (MR) imaging) and microstructure. The proposed methodology is such that once ligament morphology is measured (with MR), a researcher or clinician will immediately have a means of estimating the function of a ligament. With this classification scheme, both simple (such as clinical neuromuscular balance tests) and complex (such as computational modeling) processes can be employed to tailor diagnostics and treatment to specific patients. Thus we propose the following: Specific Aim 1: To assess independent mechanical, morphological and microstructural properties, considering population (younger and older), ligament, and strain rates dependencies. We will perform this analysis on eight pairs each (16 feet) of donor feet from two populations (younger and older). With mechanical testing, we are well versed in soft tissue isolation, tissue mechanical testing, and curve fitting. For the morphological measurements, our group has developed a novel technique of molding and casting soft tissues, to determine high resolution area measurements. Regarding the microstructural component, our group has the experience and expertise to analyze the molecular content of these tissues, as well as the fibril-level and fascicle-level organization of ligament tissues. Specific Aim 2: To identify the relationship between mechanical properties and morphology within each group (younger and older) and ligament type. Our group has performed preliminary analysis in combining morphological characteristics (length and area) with cluster analysis to determine if and to what extent ligaments can be grouped based on external appearance. Using linear mixed effects regression, a further analysis of the interrelationships between these factors will consider the relationship between ligament morphology and mechanical properties. Specific Aim 3: To identify the relationship between mechanical properties and microscopic structure within each group (younger and older) and ligament type. Using a similar linear mixed effects regression to Specific Aim 2, the relationship between microstructure and mechanical properties of ligaments will be determined. We anticipate direct benefit to ongoing experimental and computational studies. Furthermore, this foundational development motivates two future R01 proposals: (1) using MR imaging of live subjects to measure morphology and thus estimate material behavior - a stepping stone for, (2) evaluating other populations (such as diabetic) via MR to determine ankle function and injury risk.